Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 745 PM EDT Tue Jun 21 2022 Valid 12Z Sat Jun 25 2022 - 12Z Wed Jun 29 2022 ...Overview... Guidance shows a mean ridge aloft across the mainland into northwestern Canada, with only a slight eastward drift from the weekend into next week. This feature will promote above to much above normal temperatures over a majority of the state. Meanwhile an upper trough with embedded low should persist over/near the Bering Sea for most of the period, with an initial surface front anchored by Bering Sea low pressure helping to focus moisture over the eastern Aleutians and possibly extending into parts of the Alaska Peninsula and far western mainland before the front dissipates. A deep upper low initially north of Siberia is most likely to stay well northwest of the mainland but there is enough guidance spread to produce some uncertainty regarding how much its surrounding flow may influence the northern mainland. ...Guidance Evaluation/Predictability Assessment... While the models and ensembles generally highlight the three primary large scale features mentioned above, there has been a fair amount of spread for some of the details--in particular for the features to the west/northwest of the upper ridge. Most operational models have been inconsistent from run to run for specifics within the mean trough which the ensemble means have been fairly consistently keeping over the Bering Sea through the period. Of particular note, the 12Z and 18Z GFS runs have been farther west than other guidance with northern stream energy that drops down and forms that model's most persistent upper low. The 06Z GFS was closer to the model/ensemble consensus. For the Arctic low, the ensemble means have been consistent in keeping it well northwest of the mainland through the period with minimal influence from surrounding flow, so preferences lean toward that idea. GFS runs have varied considerably over the past day or so, with some earlier runs quite progressive, the 06Z/12Z runs more comparable to the means, and the 18Z run bringing it closer to the northwestern mainland by the end of the period. CMC runs have tended to be progressive (with the 12Z run being most extreme to lower heights over the northern mainland), and the 12Z ECMWF strays faster than the 00Z run. Based on guidance comparisons and ensemble mean continuity, today's forecast started with an operational model blend for the first half of the period. Inputs included the 12Z/00Z ECMWF, 06Z GFS, and 12Z UKMET/CMC. The forecast started incorporating 12Z GEFS/00Z ECMWF means after early Monday and reached a half models/half means weight by day 8 Wednesday. The remaining model input by late period tilted mostly to the 06Z GFS/00Z ECMWF. An artifact of this blend is a weak wave that reaches near the Aleutians by next Wednesday. The full array of models/ensembles would suggest this feature has lower confidence/predictability than offered by the 06Z GFS/00Z ECMWF similarity, within a broad zone where an ill-defined wavy North Pacific front could exist. ...Weather and Hazard Highlights... The slow-moving upper ridge over the mainland and northwestern Canada should promote a broad area of above to much above normal temperatures during the period. Currently expect the most notable/impactful anomalies to be over the Interior and southern Panhandle. A few pockets of below normal highs may exist close to the southern coast and over the northwestern mainland while the Aleutians will tend to be on the cool side under mean troughing aloft. A wavy front anchored by Bering Sea low pressure this weekend should produce some focused rainfall over at least the eastern Aleutians. Smaller-scale details of flow aloft within the supporting upper trough and between the trough/downstream ridging will determine how much moisture reaches the Alaska Peninsula and far western mainland. The front should dissipate by the start of next week. Expect precipitation to be lighter and more scattered over areas to the east given the prevalence of upper ridging. Weak North Pacific waviness could bring some moisture into the Aleutians by next Tuesday-Wednesday, though confidence is low for this aspect of the forecast. Rausch Hazards: - Much above normal temperatures across portions of the Alaska Panhandle and mainland Alaska, Sat-Tue, Jun 25-Jun 28. Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html